Back to EveryPatent.com
| United States Patent |
5,610,225
|
|
Farwaha
, et al.
|
March 11, 1997
|
Latex paints which are free of volatile coalescents and freeze-thaw
additives
Abstract
Freeze-thaw stable latex binders and latex paint compositions are prepared
without the use of volatile freeze-thaw additives. The latex binder
contains a polymer which is the emulsion polymerization product of a
polymerizable polyethylene glycol (PPEG) monomer, wherein the molecular
weight of the ethylene oxide moiety in the PPEG monomer is from about 175
to 1,100, at least one acrylic monomer and, optionally, one or more
styrenic, ionic or wet adhesion monomers. Methods for preparing the
freeze-thaw stable latex compositions are also disclosed.
| Inventors:
|
Farwaha; Rajeev (Brampton, CA);
Phan; Lien (Mississauga, CA);
Currie; William (Elmira, CA)
|
| Assignee:
|
National Starch and Chemical Investment Holding Corporation (Wilmington, DE)
|
| Appl. No.:
|
434098 |
| Filed:
|
May 3, 1995 |
| Current U.S. Class: |
524/558; 526/320 |
| Intern'l Class: |
C08L 033/14; C08F 220/28 |
| Field of Search: |
524/558
526/320
|
References Cited
U.S. Patent Documents
| 3896161 | Jul., 1975 | Borden et al. | 560/224.
|
| 4075411 | Feb., 1978 | Dickstein | 560/224.
|
| 4077926 | Mar., 1978 | Sanderson et al. | 524/588.
|
| 4268641 | May., 1981 | Koenig et al. | 524/588.
|
| 4322328 | Mar., 1982 | Graetz et al. | 524/458.
|
| 4668730 | May., 1987 | Iovine et al. | 524/460.
|
| 5124393 | Jun., 1992 | Ingle et al. | 524/558.
|
| 5134186 | Jul., 1992 | Ingle et al. | 524/558.
|
| 5157071 | Oct., 1992 | Ingle | 524/558.
|
| 5206286 | Apr., 1993 | Swarup et al. | 524/761.
|
| 5208285 | May., 1993 | Boyce et al. | 524/516.
|
| 5212225 | May., 1993 | Ingle | 524/558.
|
| 5219917 | Jun., 1993 | Ingle et al. | 524/558.
|
| 5227423 | Jul., 1993 | Ingle | 524/558.
|
| Foreign Patent Documents |
| 0107300 | Jan., 1983 | EP.
| |
Primary Examiner: Szekely; Peter A.
Attorney, Agent or Firm: Wissing; William K.
Claims
We claim:
1. A latex paint composition, comprising: a latex which comprises
(a) a polymer which is the polymerization product of
(i) a polymerizable polyethylene glycol monomer of Structure I
##STR2##
wherein R.sub.1 and R.sub.2 are independently H or CH.sub.3 and x is from
about 4 to 25, and wherein the polymerizable polyethylene glycol monomer
is present in an amount effective to impart freeze-thaw stability to the
latex without the use of a volatile freeze-thaw additive, up to about 2.5
pphm and wherein the molecular weight of the ethylene oxide moiety in said
polymerizable polyethylene glycol monomer is from about 200 to about 1000,
(ii) at least one acrylic monomer which is copolymerizable with the
polymerizable polyethylene glycol monomer;
(iii) 0 to 40 pphm of a styrenic monomer;
(iv) an ionic monomer present in an amount effective to impart mechanical
stability to the latex, up to 2 pphm; and
(v) 0 to 2 pphm of a wet adhesion monomer,
(b) water; and
(c) an emulsifier selected from the group consisting of anionic, cationic
and nonionic emulsifiers present in amounts effective to disperse the
polymer in the water,
wherein the polymer is present in amounts effective to function as a binder
in the latex paint composition and wherein the latex and the latex paint
composition are freeze-thaw stable and mechanically stable.
2. The latex paint of claim 1 wherein the acrylic monomer is selected from
the group consisting of C.sub.1 -C.sub.10 alkyl esters of
.alpha.,.beta.-ethylenically unsaturated C.sub.2 -C.sub.6 monocarboxylic
acids, hydroxy C.sub.1 -C.sub.4 alkyl esters of
.alpha.,.beta.-ethylenically unsaturated C.sub.2 -C.sub.6 monocarboxylic
acids, and C.sub.4 -C.sub.8 alkyl di-esters of
.alpha.,.beta.-ethylenically unsaturated C.sub.4 -C.sub.8 dicarboxylic
acids.
3. The latex paint of claim 1 wherein the latex paint is substantially free
of volatile freeze-thaw additives.
4. The latex paint of claim 1 wherein the latex paint is substantially free
of volatile coalescents.
5. The latex paint of claim 3 wherein the latex paint is substantially free
of volatile coalescents.
6. A method for preparing freeze-thaw stable latex paint compositions, the
method comprising formulating into the latex paint composition a latex
comprising:
(a) a polymer which is the polymerization product of
(i) a polymerizable polyethylene glycol monomer of Structure I
##STR3##
wherein R.sub.1 and R.sub.2 are independently H or CH.sub.3 and x is from
about 4 to 25, and wherein the polymerizable polyethylene glycol monomer
is present in an amount effective to impart freeze-thaw stability to the
latex without the use of a volatile freeze-thaw additive, up to about 2.5
pphm and wherein the molecular weight of the ethylene oxide moiety in said
polymerizable polyethylene glycol monomer is from about 200 to about 1000,
(ii) at least one acrylic monomer which is copolymerizable with the
polymerizable polyethylene glycol monomer;
(iii) 0 to 40 pphm of a styrenic monomer;
(iv) an ionic monomer present in an amount effective to impart mechanical
stability to the latex, up to 2 pphm; and
(v) 0 to 2 pphm of a wet adhesion monomer,
(b) water; and
(c) an emulsifier selected from the group consisting of anionic, cationic
and nonionic emulsifiers present in amounts effective to disperse the
polymer in the water,
wherein the polymer is present in amounts effective to function as a binder
in the latex paint composition and wherein the latex and the latex paint
composition are freeze-thaw stable and mechanically stable.
7. The method of claim 6 wherein the acrylic monomer is selected from the
group consisting of C.sub.1 -C.sub.10 alkyl esters of
.alpha.,.beta.-ethylenically unsaturated C.sub.2 -C.sub.6 monocarboxylic
acids, hydroxy C.sub.1 -C.sub.4 alkyl esters of
.alpha.,.beta.-ethylenically unsaturated C.sub.2 -C.sub.6 monocarboxylic
acids, and C.sub.4 -C.sub.8 alkyl di-esters of
.alpha.,.beta.-ethylenically unsaturated C.sub.4 -C.sub.8 dicarboxylic
acids.
8. The method of claim 6 wherein the latex paint is substantially free of
volatile freeze-thaw additives.
9. The method of claim 6 wherein the latex paint is substantially free of
volatile coalescents.
10. The latex paint of claim 8 wherein the latex paint is substantially
free of volatile coalescents.
Description
FIELD OF THE INVENTION
The present invention relates to latex binders for use in latex paints, to
latex paint compositions which are free of volatile coalescents and
volatile freeze-thaw additives and to methods of preparing such latex
compositions.
BACKGROUND OF THE INVENTION
The properties that are desirable in aqueous latex paints, namely the
ability to be used at a temperature low enough for application over a long
seasonal range, to withstand repeated cycles of freezing and thawing, and
to form a film hard enough to avoid tackiness or blocking and dirt pickup
in the intended application, are enhanced in latex-based paint
formulations by the addition of volatile coalescing solvents and
freeze-thaw additives. These coalescing solvents, for example, butyl
carbitol acetate and 3-hydroxy-2,2,4-trimethylpentyl isobutyrate, and
freeze-thaw additives, for example, propylene glycol and ethylene glycol,
are volatile organic compounds (VOC) that are present in amounts up to 360
g per liter of paint (3 lbs. per gallon), not including water. With the
universal recognition that VOCs are detrimental to the environment, there
is a need for latex-based paints that contain no volatile coalescing
solvents or freeze-thaw additives.
Latex paints employ latex binders as film formers and binders for pigments,
fillers and the like, which are used in latex paints. The latex binders
typically comprise emulsion polymers. Coalescing solvents normally are
required because the latex binders used in latex paints must have the
lowest possible film forming temperature (MFFT) and the highest possible
glass transition temperature (Tg). The MFFT is the lowest temperature at
which the polymer particles of the latex binder will mutually coalesce and
form a continuous film when the water, which is the solvent base,
evaporates. Polymers that have low MFFT extend the temperature conditions
under which the paint can be applied. The Tg is the temperature at which a
polymer changes from an amorphous, soft and tacky state to a glassy, hard,
and rigid state. Polymers with high Tg values will result in a paint
coating that will be hard, resistant to abrasion and resistant to
blocking. Volatile coalescing solvents effectively lower the Tg of the
polymer to meet the desired low MFFT on application, and then eventually
diffuse out of the paint and evaporate under normal ambient conditions of
temperature, humidity and atmospheric pressure, leaving a high Tg film.
Freeze-thaw additives are added to paint formulations simply to impart
freeze-thaw stability during transportation and storage.
The pigments or fillers present in the paint formulation result in
anti-blocking characteristics in the paint film. The relationship between
hardness of the coating and the amount of pigment is represented by
pigment volume concentration (PVC), which is the fractional volume of
pigment in a unit volume of resin. Thus, low PVC coatings, such as
semi-gloss paints, contain relatively low levels of pigment, and high PVC
coating compositions, such as satin to flat paints, contain high levels of
pigments. Polymers with low Tg and MFFT in low PVC paint formula will
exhibit blocking tendencies. On the other hand, the soft latices will show
anti-blocking characteristics in high PVC paint formulas. In low PVC paint
formulas, glass transition of the polymer (Tg) determines the hardness of
the coating. In high PVC paint formulas, pigments determine the hardness
of the coating. The Tg of the polymer can be calculated using the Fox
equation, 1/Tg (polymer)=W.sub.(a) /Tg.sub.(a) +W.sub.(b) /Tg.sub.(b) + .
. . where W.sub.(a) and W.sub.(b) are the weight fractions of comonomers
(a) and (b) and Tg.sub.(a) and Tg.sub.(b) are the glass transition
temperatures for homopolymers (a) and (b), respectively. Glass transition
temperatures for various homopolymers are available in many literature
sources, including J. Brandup and E. H. Immergut, Polymer Handbook, 2nd
ed., John Wiley & Sons, New York, pp. 139-192 (1975).
In organic-solvented paint systems, researchers have been combating the
freeze-thaw issue by using blends of surfactants in place of traditionally
employed anionic surfactants. For example, methods for making a viscosity
stable latex by blending a cationic surfactant, an amphoteric surfactant,
and a non-ionic surfactant in a prescribed ratio are known. However, the
blended system is not satisfactory in many other aspects. The preparation
of sterically stabilized latex particles by copolymerizing non-ionic
surfactants are known. The synthesis of copolymerizable esters of alkyloxy
glycols, wherein the alkyl group contains from 8 to 24 carbon atoms, and
their use as emulsifiers and stabilizers in emulsion polymerization have
been reported.
There is a growing concern about the potentially adverse environmental and
health effects of many of the volatile coalescing solvents and freeze-thaw
additives. There is a growing need for polymers, for use in latex binders
in latex paints, which will provide desired hardness properties, adequate
film formation at low temperature, and flexibility. In addition, it is
also desirable to eliminate volatile coalescents and freeze-thaw additives
from trade sale paints without compromising physical properties such as
coating hardness, low MFFT and freeze-thaw stability. Accordingly, it
would be desirable to develop polymeric latex binders, particularly
acrylic or styrene/acrylic polymer latex binders, which have the MFFT and
Tg required for use in latex paint compositions, which are free of
volatile coalescing solvents or freeze-thaw additives and which maintain
adequate freeze-thaw stability, abrasion resistance and anti-blocking
properties.
SUMMARY OF THE INVENTION
The present invention is directed to latex paint compositions which are
free of volatile coalescing solvents and freeze-thaw additives and which
comprise a latex binder which contains a polymer which is the emulsion
polymerization product of a polymerizable polyethylene glycol (PPEG)
monomer, at least one acrylic monomer and, optionally, one or more
monomers selected from the group consisting of styrenic monomers, ionic
monomers and wet adhesion monomers. The invention is also directed to
methods of preparing freeze-thaw stable latex paint compositions without
the use of volatile freeze-thaw additives and to the freeze-thaw stable
latex binders.
DETAILED DESCRIPTION OF THE INVENTION
The latex binders according to the present invention must have a MFFT of
less than 5.degree. C., yet provide sufficient abrasion resistance in
order to function as a binder in the latex paint composition according to
the present invention. Generally, the level of abrasion resistance
required of a latex paint will depend upon the anticipated end-use of the
paint. More abrasion resistance is required where the conditions under
which the paint must endure are more severe. Additionally, the latex
binders and the paint compositions must be freeze-thaw stable, meaning
that they survive five freeze-thaw cycles. Finally, the paint compositions
must be resistant to blocking.
According to the present invention, it has been discovered that freeze-thaw
stable, polymeric latex binders which have a MFFT of less than 5.degree.
C. and which provide sufficient abrasion and blocking resistance required
for use as a latex binder in latex paint compositions according to the
present invention may be prepared without the use of volatile coalescents
or freeze-thaw additives. "Volatile coalescent" and "volatile freeze-thaw
additive", as used herein, refer to those coalescents and freeze-thaw
additives which diffuse out from the applied film of the latex paint and
evaporate under typical ambient conditions. By typical ambient conditions,
it is meant those conditions of temperature, humidity and barometric
pressure under which latex paints are typically applied and cured.
The term "latex" is used herein in its conventional meaning, i.e. a
dispersion of particulate matter in an aqueous phase which contains an
emulsifier or surfactant suitable for preparing the latex. Latex binders,
as used herein, comprise a polymer dispersed in an aqueous phase with an
appropriate emulsifier or surfactant.
According to one embodiment of this invention, there are provided polymeric
latex binders which comprise acrylic or styrene/acrylic polymers which are
the polymerization products of a polymerizable polyethylene glycol (PPEG)
monomer of structure I
##STR1##
wherein R.sub.1 and R.sub.2 are independently H or CH.sub.3 and x is from
about 4 to 25, and at least one acrylic monomer. The polymers may further
comprise 0 to 40 pphm of the polymerized residue of optional styrenic
monomers, such as styrene, halogenated styrene and alkyl-substituted
styrene. Other optional monomers include ionic monomers to impart
mechanical stability and monomers to enhance wet adhesion. In a second
embodiment of the invention, latex paint compositions utilize the latex
binders of the present invention in amounts effective to provide a latex
paint which is freeze-thaw stable, which has a MFFT of less than 5.degree.
C. and which has sufficient abrasion and blocking resistance for its
intended use.
The latex binders of this invention are particularly advantageous for use
in aqueous coating compositions. The first advantage of these binders is
that they permit the formulation of aqueous coatings having adequate film
formation and a desirable balance of hardness. The second advantage is
that they can be used to formulate latex paints which require no
freeze-thaw additive, such as ethylene glycol or propylene glycol, yet
which exhibit excellent freeze-thaw stability. It is preferred that the
latex binders and the latex paints of the present invention be
substantially free of any volatile coalescing solvent or volatile
freeze-thaw additive. More preferably, the binders and paints will be free
of any volatile coalescing solvent or volatile freeze-thaw additive. One
will recognize that small amounts of either volatile coalescing solvents
or freeze-thaw additives may be added if desired, although they should not
be present in any appreciable amounts and are not required in the present
invention.
The molecular weight of the ethylene oxide (EO) moiety contained in the
PPEG monomer is from about 175 to about 1,100, preferably from about 200
to about 1,000. More preferably the EO molecular weight is less than about
900 and most preferably from about 200 to 880. As the molecular weight of
the EO is increased to greater than about 1,100, poor block resistance is
exhibited in the latex paint composition. The PPEG monomer is used in
amounts effective to impart freeze-thaw stability to the latex binder
without the use of a volatile freeze-thaw additive. The amount of PPEG
monomer required depends on factors such as pigment/volume concentration,
relative hydrophilicity of the polymer, surfactant systems and the like.
One skilled in the art, once armed with the present specification, would
be able to determine how much PPEG should be used to prepare a particular
latex binder to be used in a particular latex paint. Preferably, the
polymer will comprise the polymerized residue of from about 1 to 2.5 parts
by weight of the PPEG monomer per 100 parts by weight of total monomer(s)
used to prepare the polymer (pphm).
The polymer also comprises the polymerized residue of at least one acrylic
monomer which is copolymerizable with the PPEG monomer. The acrylic
monomer is selected from the group consisting of C.sub.1 -C.sub.10 alkyl
esters of .alpha.,.beta.-ethylenically unsaturated C.sub.2 -C.sub.6
monocarboxylic acids; hydroxy C.sub.1 -C.sub.4 alkyl esters of .alpha.,
.beta.-ethylenically unsaturated C.sub.2 -C.sub.6 monocarboxylic acids;
and C.sub.4 -C.sub.8 alkyl di-esters of .alpha.,.beta.-ethylenically
unsaturated C.sub.4 -C.sub.8 dicarboxylic acids. Preferably, the acrylic
monomer is selected from the group consisting of C.sub.1 -C.sub.10 alkyl
esters of acrylic and methacrylic acid and C.sub.4 -C.sub.8 alkyl
di-esters of maleic, itaconic and fumaric acids. Preferably, at least one
C.sub.1 -C.sub.8 alkyl ester of acrylic acid is utilized. Particularly
preferred acrylic monomers include methyl acrylate, ethyl acrylate, butyl
acrylate, 2-ethyl hexyl acrylate, decyl acrylate, methyl methacrylate,
butyl methacrylate, i-butyl methacrylate, i-bornyl methacrylate, hydroxy
ethyl acrylate, hydroxy ethyl methacrylate.
The polymer may also comprise 0 to 2 pphm of the polymerized residue of an
ionic monomer. In preferred embodiments, not more than about 1 pphm of the
ionic monomer is used. The ionic monomers are utilized to impart
mechanical stability to the latex binder and the latex paints, i.e., they
are stable upon application of shear to the latex binders or paints, such
as during pumping of the latex binder and/or the paint compositions during
processing and during addition of the latex binder to the "grind" portion
of the paint formulation during the preparation thereof. The "grind" is
that portion of the paint formulation which includes the pigments, fillers
and the like. The pigments and fillers are "ground" using conventional
mixing techniques, to a particular Hegman dispersion value. The grind is
then "let down", that is, the balance of the paint composition, including
the latex binder and any balance of water, are added to the grind and
mixed. Typical classes of ionic monomers include, but are not limited to,
.alpha.,.beta.-ethylenically unsaturated C.sub.3 -C.sub.8 monocarboxylic
and C.sub.4 -C.sub.8 dicarboxylic acids, including the anhydrides thereof,
and the C.sub.4 -C.sub.8 alkyl half-esters of the
.alpha.,.beta.-ethylenically unsaturated C.sub.4 -C.sub.8 dicarboxylic
acids. Exemplary ionic monomers include acrylamido methyl propane,
sulfonic acid, styrene sulfonate, sodium vinyl sulfonate, acrylic acid and
methacrylic acid, and the C.sub.4 -C.sub.8 alkyl half esters of maleic
acid, maleic anhydride, fumaric acid, and itaconic acid. Particularly
preferred ionic monomers include acrylic acid and methacrylic acid.
In order to optimize the wet adhesion of the latex paint formulation, the
polymer may comprise 0 to 2 pphm of the polymerized residue of a wet
adhesion monomer, or a combination of wet adhesion monomers. These
monomers are well known in the art and include aminoethyl acrylate and
methacrylate, dimethylaminopropyl acrylate and methacrylate,
3-dimethylamino-2,2-dimethylpropyl-1-acrylate and methacrylate,
2-N-morpholinoethyl acrylate and methacrylate, 2-N-piperidinoethyl
acrylate and methacrylate, N-(3-dimethylaminopropyl) acrylamide and
methacrylamide, N(3-dimethylamino-2, 2-dimethylpropyl)acrylamide and
methacrylamide, N-dimethylaminomethy) acrylamide and methacrylamide,
N-dimethylaminomethyl acrylamide and methacrylamide,
N-(4-morpholino-methyl) acrylamide and methacrylamide, vinylimidazole,
vinylpyrrolidone, N-(2-methacryloyloxyethyl) ethylene urea,
N-(2-methacryloxyacetamidoethyl)-N, N'-ethyleneurea, allylalkyl ethylene
urea, N-methacrylamidomethyl urea, N-methacryoyl urea,
N-[3-(1,3-diazacryclohexan)-2-on-propy]methyacrylamide,
2-(1-imidazolyl)ethyl methacrylate,
2-(1-imidazolidin-2-on)ethylmethacrylate, N-(methacrylamido)ethyl urea
(DV2422, Rhone-Poulenc) and allyl ureido wet adhesion monomer (Sipomer
WAM.RTM., Rhone Poulenc). When used, the wet adhesion monomer will be
present in an amount from 0.2% to 2.0% pphm.
The emulsion polymerization of the polymer can be accomplished by known
procedures for polymerization in aqueous emulsion. Optionally,
conventional seeding procedures can be employed to aid in controlling
polymerization to achieve the desired average particle size and particle
size distribution. If seeding is employed, the polymer seed will be
present in amounts that correspond to about 0.1% to 8% by weight of the
total polymer, and will range in size from about 20% to 60% of the
diameter of the polymer particles to be formed.
The seed latex can constitute a previously prepared latex or polymer
powder, or it can be prepared in situ. The monomeric composition of the
seed latex can vary; however, it is preferable that it be substantially
the same as that of the polymer.
The monomer or comonomers and, optionally, the seed to be employed in the
preparation of the polymer, are dispersed into water with agitation
sufficient to emulsify the mixture. The aqueous medium may also contain a
free radical polymerization catalyst, an emulsifying agent (i.e.,
surfactant), or other ingredients that are known and conventionally
employed in the art as emulsion polymerization aids.
Suitable free radical polymerization catalysts are the catalysts known to
promote emulsion polymerization and include water-soluble oxidizing
agents, such as, organic peroxides (e.g., t-butyl hydroperoxide, cumene
hydroperoxide, etc.), inorganic oxidizing agents (e.g., hydrogen peroxide,
potassium persulfate, sodium persulfate, ammonium persulfate, etc.) and
those catalysts that are activated in the water phase by a water-soluble
reducing agent. Such catalysts are employed in a catalytic amount
sufficient to cause polymerization. As a general rule, a catalytic amount
ranges from about 0.1 to 5 pphm. As alternatives to heat or catalytic
compounds to activate the polymerization, other free radical producing
means, such as exposure to activating radiation, can be employed.
Suitable emulsifying agents include anionic, cationic, and nonionic
emulsifiers customarily used in emulsion polymerization. Usually, at least
one anionic emulsifier is utilized and one or more nonionic emulsifiers
may also be utilized. Representative anionic emulsifiers are the alkyl
aryl sulfonates, alkali metal alkyl sulfates, the sulfonated alkyl esters,
and fatty acid soaps. Specific examples include sodium dodecylbenzene
sulfonate RHODACAL2DS-4, sodium butylnaphthalene sulfonate, sodium lauryl
sulfate, disodium dodecyl diphenyl ether disulfonate, N-octadecyl disodium
sulfosuccinate and dioctyl sodium sulfosuccinate. The emulsifying agents
are employed in amounts to achieve adequate emulsification and to provide
desired particle size and particle size distribution.
Other ingredients known in the art to be useful for various specific
purposes in emulsion polymerization, such as, acids, salts, chain transfer
agents, and chelating agents, can also be employed in the preparation of
the polymer. For example, if the polymerizable constituents include a
monoethylenically unsaturated carboxylic acid monomer, polymerization
under acidic conditions (pH 2 to 7, preferably 2 to 5) is preferred. In
such instances, the aqueous medium can include those known weak acids and
their salts that are commonly used to provide a buffered system at the
desired pH range.
The manner of combining the polymerization ingredients can be by various
known monomer feed methods, such as, continuous monomer addition,
incremental monomer addition, or addition in a single charge of the entire
amount of monomers. The entire amount of the aqueous medium with
polymerization additives can be present in the polymerization vessel
before introduction of the monomers, or alternatively, the aqueous medium,
or a portion of it, can be added continuously or incrementally during the
course of the polymerization.
Polymerization is initiated by heating the emulsified mixture with
continued agitation to a temperature usually between about 50.degree. to
100.degree., preferably between 60.degree. to 100.degree. C.
Polymerization is continued by maintaining the emulsified mixture at the
selected temperature until conversion of the monomer or monomers to
polymer has been reached.
Following polymerization, the solids content of the resulting aqueous
heterogeneous polymer latex can be adjusted to the level desired by the
addition of water or by the removal of water by distillation. Generally,
the desired level of polymeric solids content is from about 20 to 60% by
weight on a total weight basis.
The size of the polymer particles can vary; however, for optimum water
resistant, it is preferable that the particles have an average diameter of
less than 500 nanometers. In general, for the polymer of this invention,
the smaller the average particle size, the more water resistant the
polymer. Suitable particle sizes generally can be achieved directly from
the polymerization. However, screening of the resulting latex to remove
particles outside the desired size range, and thus narrowing the particle
size distribution, may be employed.
For various applications, it is sometimes desirable to have small amounts
of additives, such as, surfactants, bactericides, pH modifiers, and
antifoamers, incorporated in the latex. This may be done in a conventional
manner and at any convenient point in the preparation of the latexes.
The paints are formulated using techniques known to those skilled in the
art of manufacturing paint. Generally, water, defoamer, stabilizer,
pigment, filler and surfactant are combined to form the grind, where the
pigments and fillers are ground to a desired particle size as indicated by
a Hegman reading of 2 to 3. Additional water, latex binder, rheology
modifiers, biocides and the like are added to the grind and the entire
batch is blended and adjusted to desired Hegman readings and viscosity.
The following test procedures and organic-solvent-free, semi-gloss latex
paint formulation were used to evaluate the latex binders and latex paints
of the present invention.
Test Procedures
Blocking Resistance
Six mil films (1 mil=25 microns) were cast over leneta 3-B Opacity charts
and allowed to dry at constant temperature and humidity (22.degree. C. and
40 to 60% relative humidity) for 7 days. At the end of the first, second
and seventh days, two portions of the coated charts were placed
face-to-face and subjected to 0.070 kg/cm.sup.2 (1 psi) pressure for 1 day
at a constant temperature of 22.degree. C. and 40 to 60% relative
humidity. At the end of the seventh day, an additional two pieces of the
chart were subjected to 0.070 kg/cm.sup.2 (1 psi) in a 35.degree. C. oven
for 30 minutes. Blocking resistance was determined visually when the
panels were pulled apart with manual force and rated as follows:
______________________________________
Blocking Resistance
Numerical Rating
Type of Separation
______________________________________
10 no tack
9 trace tack
8 very slight tack
7 very slight to slight tack
6 slight tack
5 moderate tack
4 very tacky
3 film ruptures 5 to 25% when pulled apart
2 film ruptures 25 to 50% when pulled apart
1 film ruptures 50 to 75% when pulled apart
0 film ruptures 75 to 100% when pulled apart
______________________________________
Low Temperature Film Formation
The paint composition was conditioned in a 2.degree. to 5.degree. C.
refrigerator for 1 hour, and a 3 mil film of the paint then applied over a
19 BR leneta chart. The film was allowed to dry overnight at 2.degree. to
5.degree. C. and visually examined for signs of cracking. A paint was
deemed to form acceptable films when no difference could be seen between
the film applied at 5.degree. C. and a film applied at room temperature
(22.degree. C.).
Abrasion Resistance (Scrubability) ASTM 24860
A test scrub panel was prepared by drawing a 7.0 mil film of paint on a
leneta chart and allowing the paint to dry for 7 days in an open room kept
at 23.degree..+-.2.degree. C. and 50.+-.5% relative humidity. The dried
chart was affixed to a glass panel and put into a scrub machine equipped
with a scrub brush and a basin for holding the test panel. The brush was
prepared by immersing it overnight in 2% solution of Triton.RTM.X-100
surfactant. The brush was placed in the machine holder and the test scrub
panel was put under the brush. The brush bristles were spread evenly with
10 grams of a standardized scrub medium (available from Leneta Co.). The
panel was then wet with 5 ml of reagent water in the path of the brush.
The scrub machine was started. After every 800 strokes before failure, 10
grams of scrub medium and 5 ml of reagent water were added to the brush
bristles. The number of strokes to the paint at which 0.5 inch of black
chart shows through the test panel was recorded.
Freeze-Thaw Stability Test
The paint sample was transferred into a 250 ml stainless steel can and was
kept in the freezer for 18 hours at -18.degree. C. Then the sample was
removed from the freezer and was allowed to thaw for 24 hours to room
temperature. The sample was observed for flow properties, lump formation,
and coagulation. The sample was considered to pass if it exhibited no
coagulation. This cycle of freezing-thawing was repeated until either the
paint coagulated or until a total of five cycles were completed with no
coagulation.
Wet Adhesion
Scrub panels were prepared by drawing down a 3 mil film of a semi-gloss
alkyd base (chosen as being the most difficult test for wet adhesion) onto
a leneta chart. The charts were aged at least one week at room
temperature. The test latex paints were then drawn down into a 3 mil film
onto the aged alkyd surface and allowed to dry for 48 hours. The dried
charts were affixed to glass panels and put into the scrub machine
equipped with a scrub brush and a basin for holding the panel. The brush
was conditioned by immersing it in warm water for 30 minutes and then
placed in the machine holder. The test panel was placed in the basin under
the brush and 200 g of warm (50.degree. C.) water were added to the basin.
The scrub machine was started and run for 400 strokes. If the coating
remained intact, 8 gm of a dry abrasive (Ajax.RTM.) were placed under the
brush and the machine run for another 100 strokes. The last step was
repeated until the coating failed, that is, when the test paint stripped
from the alkyd base. The number of strokes to failure was recorded.
______________________________________
Solvent Free Semi-Gloss Paint Formula
Pounds per 100 U.S.
Gallon
______________________________________
Water 125.0
BYK .RTM. 155 dispersant
4.5
BYK .RTM. 034 defoamer
2.0
Surfynol .RTM. CT-111
2.5
Potassium Hydroxide 45%
2.5
Kronos 2020 250.0
ASP 170 45.0
Polyphobe .RTM. 102
4.0
Disperse 5 to 6 Hegman
Water 130.0
Polyphobe .RTM. X9823
25.0
Latex binder (50% Solids)
500.0
Igepal .RTM. CO-630
1.5
Kathon LX 0.4
BYK 034 2.0
1093.9
______________________________________
PVC 27.2%
Weight Solids 51.27%
Volume Solids 36.81%
Pounds per U.S. Gallon 10.87
60.degree. Gloss 55
Source
1. BYK.RTM. 155 dispersant is a solution of sodium salt of an acrylic acid
copolymer, available from BYK Chemie.
2. BYK.RTM. 034 defoamer is a proprietary mixture of hydrophobic components
in paraffin based mineral oil, silicone containing, available from BYK
Chemie.
3. Surfynol.RTM. CT-111 surfactant is an ethylene oxide adduct of
acetyleneic glycols, available from Air Products.
4. Kronos 2020 is rutile titanium dioxide, available from Kronos, Inc.
5. ASP-170 is aluminum silicate pigment, available from Engelhard
Corporation.
6. Polyphobe is a proprietary urethane associative thickener, available
from Union Carbide.
7. Igepal CO-630 is a nonylphenol ethoxylate non-ionic surfactant,
available from Rhone-Poulenc.
8. Kathon LX is a microbiocide having active ingredients of
5-chlor-2-methyl-4-isothazolin-3-one and 2-methyl-4-isothazolin-3-one
present in an amount up to 14% available from Rohm & Haas.
9. Hegman is a unit of grind used in the industry.
EXAMPLE I
An acrylic latex binder was prepared according to the formula and procedure
given below.
______________________________________
Ingredients Concentration in pphm
______________________________________
Water 34.3
Monomer Mix
Water 36.6
Dodecylbenzene Sulfonate (23%)
4.3
Methacrylic Acid 0.8
Sipomer WAM2 1.0
Methyl methacrylate (MMA)
41.9
Butyl acrylate (BA)
56.3
Catalyst Solution
Water 18.0
Ammonium persulfate
0.4
______________________________________
In a 3 liter vessel, equipped with a reflux condenser, addition funnels,
and stirrer. An initial water charge was added to the reactor with
agitation at 100 rpm. The reactor was heated to 78.degree. C. A 22 grams
portion of the monomer mix and 14 grams of the catalyst solution were then
charged to the reaction vessel and the reaction mixture was held for 20
minutes at 78.degree. C. The remainder of the monomer mix was metered into
the reaction over a period of 4 hours. The catalyst solution was metered
to the reactor over a period of 4.5 hours. The reaction was then held for
10 minutes at 78.degree. C. and was cooled to room temperature. As the
reaction mixture was cooling down, 0.3 gram of t-butyl hydroperoxide in 5
grams of water and 0.3 gram of sodium formaldehyde sulfoxylate were added
when the temperature of reaction was at 65.degree. C. The pH of the
dispersion latex was adjusted to between 7 to 8 by the addition of 26.6%
aqueous ammonium hydroxide solution.
The resulting comparative latex binder was designated 1A and had the
following physical properties: 50.49% solids, particle size of 268 nm, pH
of 7.5 and MFFT of .about.0.degree. C.
Comparative latex binders 1B and 1C were prepared using the same procedure
as described in Example I, except that the amount of methacrylic acid was
increased to 2 pphm and 3 pphm, respectively. The physical properties of
latexes 1A-1C are given in Table 1. Latex binders 1A through 1C were
formulated in the volatile solvent-free, semi-gloss paint formulation and
were tested for freeze-thaw stability. Paint compositions containing latex
binders 1A and 1C were tested for abrasion resistance. Results are set
forth in Table 1.
TABLE 1
______________________________________
Latex Binder 1A 1B 1C
______________________________________
Methacrylic acid (MAA).sup.a
1.0 2.1 3.0
Freeze-thaw Stability
failed failed 3rd
passed 5 cycles
cycle
% Solids 50.49 50.3 50.42
P.S. (nm) 268 273 275
Abrasion Resistance
950 160
(Strokes to Failure)
______________________________________
.sup.a pphm
The data shows that the level of methacrylic acid required to obtain a
freeze-thaw stable latex paint which contains no volatile freeze-thaw
additive must be at least 3 pphm. However, as the data also shows, when
the level of methacrylic acid is increased to form a freeze-thaw stable
latex binder (1C), the abrasion resistance is dramatically reduced. It is
apparent, then, that balanced properties of freeze-thaw stability and
abrasion resistance must be considered in formulating the latex paint
compositions.
EXAMPLE II
A series of acrylic latex binders, designated as 1 D, 1 E, 1F and 1 G, was
prepared using the procedure and monomer composition as described in
Example I, except that each latex binder contained methoxy polyethylene
glycol methacrylate or polyethylene glycol methacrylate (PPEG monomer)
with the molecular weight of ethylene oxide ranging from 220 to 1760. The
latex binders also contain a Sipomer WAM2 wet adhesion monomer. The level
of PPEG monomer (pphm) used in preparing the latex binder compositions and
physical properties of the latex binders are given in Table 2.
TABLE 2
______________________________________
Latex Binder 1D 1E 1F 1G
______________________________________
Polyethylene glycol 1.5
methacrylate (MW of EO = 220).sup.a
Polyethylene glycol 1.5
methacrylate (MW of EO = 440).sup.a
Methoxy Polyethylene glycol 1.5
methacrylate (MW of EO = 880).sup.a
Methoxy Polyethylene glycol 1.5
methacrylate (MW of EO = 1760).sup.a
Physical Properties:
% Solids 50.17 51.3 51.4 51.8
P.S. (nm) 284 279 323 261
______________________________________
.sup.a pphm
Latexes 1D, 1E, 1F and 1G were formulated in the semi-gloss solvent-free
paint formula and were tested for abrasion resistance, wet adhesion,
freeze-thaw stability, and block resistance. The results are set forth in
Table 3.
TABLE 3
__________________________________________________________________________
Properties of Paint Formulations
Latex Binder
1D 1E 1F 1G 1C
__________________________________________________________________________
EO molecular weight
220 440 880 1760
Film formation @
smooth
smooth
smooth
smooth
smooth
<5.degree. C.
Abrasion Resistance
580 448 362 340 160
(strokes to failure)
Wet Adhesion
1500 1500 1100 900 800
(strokes to failure)
Freeze-thaw Stability
passed 5
passed 5
passed 5
passed 5
passed 5
cycles
cycles
cycles
cycles
cycles
Block Resistance
25/40.degree. C.
1 day 4/3 4/3 5/3 3/0 0/0
4 days 8/5 6/4 3/5 1/0 0/0
7 days 8/6 7/4 5/3 3/1 0/0
__________________________________________________________________________
The data in Table 3 show that as the molecular weight of ethylene oxide in
the PPEG monomer increases above 880, properties such as abrasion
resistance, wet adhesion, and block resistance tend to decrease. One
skilled in the art will recognize that these properties may be improved to
some extent by the addition of emulsifiers and/or dispersant systems to
the paint formulation. Additionally, pigment volume concentration may be
adjusted for the same purpose.
EXAMPLE III
Latex binder 1H was synthesized using the same procedure as described in
Example 2, except that the monomer composition comprised styrene/methyl
methacrylate/butyl acrylate; 10/32.5/57.5 weight %, respectively. Latex 1H
had 51.20% solids, particle size of 224 nm, pH of 7.5 to 8.0 and MFFT
.about.0.degree. C.
EXAMPLE IV
An acrylic latex binder was prepared by using a two-stage emulsion
polymerization technique. The formula and procedure are given below.
______________________________________
Concentration in
Ingredients Grams PPHM
______________________________________
Initial Water 256.3 33.6
Monomer Mix #1
Water 169.81 27.3
Rhodacal DS-4* 20.17 2.65
Methacrylic Acid
3.16 0.41
Sipomer WAM2 6.83 0.90
MMA 145.83 19.0
BA 309.80 40.6
Catalyst Solution
Water 134.76 17.7
Ammonium persulfate
3.0 0.40
Monomer Mix #2
Water 104.05 143.7
Rhodacal DS-4 12.37 1.62
Methacrylic Acid
1.94 0.25
Sipomer WAM2 4.19 0.55
MMA 161.99 22.3
BA 117.29 15.4
PEG (200 11.02 1.44
mw)methacrylate
______________________________________
*anionic surfactant available from RhonePoulenc.
Procedure
Into a 3 liter vessel, equipped with a reflux condenser, addition funnels
and stirrer, an initial water charge was added with agitation at 100 rpm.
The reactor was heated to 78.degree. C. A 22 grams charge of monomer Mix
#1 and 14.0 g of the catalyst solution were then charged to the reaction
vessel and the reaction mixture was held for 20 minutes for seed formation
at 78.degree. C. The remainder of monomer Mix #1 was added over 21/2
hours. The catalyst solution was added over a period of 4.5 hours. The
reactor content was then held at 78.degree. C. for 10 minutes. Monomer Mix
#2 was added to the reactor over 11/2 hours. At the completion of catalyst
solution addition, the reactor content was cooled to room temperature. As
the reaction mixture was cooling down, a mixture of 0.3 gram of t-butyl
hydroperoxide in 5 grams of water, and 0.3 gram of sodium formaldehyde
sulfoxylate in 10 grams of water were added when the temperature was at
65.degree. C. The pH of the emulsion was adjusted to between 7 to 8 by the
addition of 26.6% aqueous ammonium hydroxide solution.
The resulting latex was designated as latex 1I and had the following
physical properties: 51.1% solids, particle size of 259 nm, pH of 8.0 and
MFFT of .about.0.degree. C.
Latexes 1H and 1I were formulated into the semi-gloss, solvent-free paint
formula and were tested for abrasion resistance, wet adhesion, block
resistance and freeze-thaw stability. Results are set forth in Table 4.
TABLE 4
______________________________________
Properties of Paint Formulations
Latex 1H 1I 1D
______________________________________
Abrasion resistance (strokes to
840 354 580
failure)
Wet adhesion (strokes to failure)
2200 1550 1500
Freeze-thaw Stability
passed 5 passed 5 passed 5
cycles cycles cycles
Block resistance 22.degree. C./40.degree. C.
1 day 4/3 4/3 4/3
4 days 8/6 8/4 8/5
7 days 8/6 8/5 8/6
______________________________________
The results in Table 4 show that when the PPEG monomer is polymerized in
the styrene/acrylic latex binder (1H), the latex paint properties such as
abrasion resistance and wet adhesion are dramatically increased while
maintaining the freeze/thaw stability and block resistance.
EXAMPLE V
A series of acrylic latex binders was prepared with the same procedure
described in Example 2, but with different copolymerizable surfactants to
study the effect of hydrophobicity of copolymerizable monomers on
freeze-thaw stability. The monomer compositions and physical properties
are shown in Table 4. The latex binders were formulated in the solvent
free, semi-gloss paint formula and tested for freeze-thaw stability.
Results are set forth in Table 5.
TABLE 5
______________________________________
1J 1K 1L 1M
______________________________________
Allyl alcohol proproxylate.sup.a
1.5
Behenyl polyethoxy ethyl 1.5
methacrylate.sup.a (MW of EO =
1100)
Ethoxylated nonyl phenol 1.5
acrylate.sup.a
(MW of EO = 176)
Poly propylene glycol mono 1.5
acrylate.sup.a
(MW of PO = 348)
Physical Properties:
Freeze-thaw Stability
Failed Failed Failed
Failed
% Solids 49.1 51.0 50.8 50.5
P. S. (nm) 261 255 283 281
______________________________________
.sup.a pphm
The results in Table 5 show that if the copolymerizable surfactant monomer
is too hydrophobic, the latex binders (1K, 1L, 1M and 1J) exhibit poor
freeze-thaw stability.
EXAMPLE VI
An acrylic latex binder was prepared using the same procedure as described
in Example I, but with 1 pphm of an anionic surfactant and 3 pphm of a
non-polymerizable, non-ionic surfactant which contains an ethylene oxide
moiety having molecular weight of 1760. The latex was designated 1N, which
had the following physical properties: 50% solids, the particle size of
153 nm, pH of 8.0 and a MFFT of .about.0.degree. C.
Latex 1N was formulated into the semi-gloss, solvent-free formula and was
tested for abrasion resistance, wet adhesion, block resistance, and
freeze-thaw stability. The results are set forth in Table 6.
TABLE 6
______________________________________
Latex 1N 1D
______________________________________
Anionic Surfactant X
Anionic Nonionic Surfactant Blend
X
polyethylene glycol methacrylate
X
(MW of EO = 220)
Abrasion resistance (strokes to failure)
800 580
Wet Adhesion (strokes to failure)
2100 1500
Freeze-thaw Stability Passed 5 Passed 5
cycles cycles
Block Resistance (25.degree. C./40.degree. C.)
1 day 0/0 4/3
4 days 0/0 8/5
7 days 0/0 8/6
______________________________________
From this data, it is shown that when a blend of anionic and non-ionic
surfactants is used to prepare a latex binder, the blocking resistance of
the formulated latex paint is completely destroyed. However, where the
nonionic PPEG monomer is polymerized with the acrylic monomers in the
presence of an anionic surfactant, the blocking resistance is maintained.
Top